There is already known from DE 10 2008 018 085 A1 an active muffler for an exhaust gas system of an internal combustion engine. This describes an active muffler for an exhaust gas system in a multiple-shell housing, having a cup-shaped top shell and a cup-shaped bottom shell. Moreover, a connection pipe branch is provided, which is led through the bottom shell and out from the housing. The branch pipe serves for connecting the muffler to an exhaust gas conducting line of the exhaust gas system.
A sound generating system is known from U.S. Pat. No. 6,959,094 B1 which composes or synthesizes on the basis of a real vehicle model several components of the vehicle sound independently of each other, and then combines these into the final sound. The individual sound is generated here by means of characteristic operating parameters of the vehicle, while the final combination of the different sounds is assembled through a mixer or equalizer. With the proposed system it is not necessary to record vehicle sounds and provide them through a storage unit.
From U.S. Pat. No. 6,005,957 A there is known an AND (Active Noise Design) system, having a loudspeaker decoupled from the exhaust gas flow and a microphone. Through the microphone, an actual variable of the emitted sound of the loudspeaker and the exhaust gas system is detected. On the basis of this actual variable, a nominal value is determined for the loudspeaker signal through a feedback control circuit with actual vs. nominal comparison and put out to the loudspeaker.
As prior art for the emergence level, one should cite a publication in the context of the 16th International Congress on Sound and Vibration, Krakow, 5-9 Jul. 2009; “3 CYLINDERS PETROL ENGINES TAILPIPE SOUND QUALITY PROCESSED THROUGH AN ORIGINAL HEARING MODEL”. This describes, under section 3, how a sound at times is not even audible, or only partly audible, due to masking effects, either through background noises or the interplay of several sounds. It defines for this an emergence level, whose magnitude is a measure of the audibility of a sound. If it is smaller than or equal to zero, then the sound is masked and is not subjectively audible. If it is greater than zero, then the “emergence level” indicates with what level or what loudness the sound is subjectively perceived.
The problem which the invention proposes to solve is to modify and dispose a sound system for a motor vehicle so that an improved sound impression, reduced costs, and a more variable application are assured.
The coupling of the sound system to the exhaust gas system, such as has been conventional thus far in the prior art, results in an immediate overlayering of the real engine sound, i.e., the engine sounds based on the exhaust gas, and the engine sounds emulated by the sound system within the exhaust gas flow, which is beneficial for the sound impression, at least as regards the sound source. It is generally known that, with the coupling of the sound system to the exhaust gas system, further influences need to be considered, involving the direct contact with the exhaust gas, especially the formation of condensate, the exhaust gas temperature, and the exhaust gas pressure, and that is mentioned here merely for sake of completeness.
However, the technical world was largely of the belief that a decoupling of the sound system, e.g. in order to circumvent the aforementioned influences, would lead to a worse sound impression.